Purification of magnesium and its alloys



Patented 1.... s, 1929.

UNITED STATES PATENT OFFICE.

GILBERT MICHEL, OF BAGNEUX, FRANCE, ASSIGNOR TO HARTO, BERG, O]? PARIS,

' FRANCE.

runm'rcarron or maennsrum- AND rrs ALLOYS.

No Drawing. Application filed February 5, 1925, Serial No.'7, 156, anr1 in France October 4, 1924.

Crude magnesium obtained either as re covery from waste or from the vessels inelectrolytic manufacture, contains in almost all cases numerous impurities and especially oxides and oxychlorides dispersed. in the mass in the state of grains or granules. It is particularly ditlicult to wholly remove the oxides. In certain former processes the purification of the magnesium was attempted by causing magnesium chloride to act upon the molten metal bath, assistedby an energetic stirring. In the case where the chloride'of magnesium was added in excess there was added thickening bodies such as fluorides of calcium or aluminum and other bodies the purpose of which was to form complexes with the chloride in excess.

But processes of this sort. present the inconvenience that it is practically impossible to know in advance the quantity of chloride necessary to saturate the impurities and furthermore there always remains in the bath, in spite of all precautions, traces of chlorides or oxychlorides which is very harmful to the metal. Even if magnesium chloride and magnesium fluorideare added together, satisfactory results would not be secured.

The presentinvention has for its object a process in which the impurities instead of being eliminated by the addition of a chloride acting as a principal purifying agent, are eliminated by the addition of magnesium fluoride without magnesium chloride. The fluoride in this case does not act to saturate magnesium chloride which only exists in traces in the bath since no additional quantities are added during the process, but it acts as a principal purifying agent for .the impurities and principally of the oxides containedin the mass.

Attempts have also been made to overcome this ditficulty by lowering the melting point of the magnesium or its alloys to the minimiun by the addition of zinc, but it is found that zinc can be alloyed with magnesium only with great ditliculty and furthermore magnesium alloyed. with zinc is found to deteriorate in the course of time. The metal or alloy which is thus obtained is of an unstable character and loses its useful qualities and mechanical properties after a time. It has been observed that the above mentioned alloy-is the less adapted for forging, rolling and the like thermo-mechanical operations employed in metal working, according as the proportion of zinc is larger. It is also found that such metals and alloys are not adapted for autogcnous welding.

It is a known fact that magnesium or its alloys which are produced by the known methods always contain traces of chlorides and oxychlorides, these being prejudicial to vention are therefore particularly adapted to all the thermo-mechanical operations em ployed'm metal working, such as forging,

"rolling and the like, and which according to their composition possess qualities of hardness, elasticity, ductility and the like of a particularly valuable kind, these products being .also capable of autogenous welding.

melting point of magnesium 1n the same man-- ner as zinc, whlch latter has been hitherto employed for this purpose, and by its use I am enabled to proceed with the operations of melting, refining and purifying under favorable conditions, avoiding all spontaneous ignition and excessive oxidation. The presence of calcium in small quantities in the magnesium does not affect its useful properties, but on the contrary alloys are obtained which are of extreme lightness combined with great hardness. The proportions which are found to produce the best results are 0.05% up to 0.3% of Ca. Magnesium containing calcium and magnesium alloys containing containing calcium have been found to be very well adapted for autogenous welding.

Due to the elimination of'all impurities containing chlorine such as the chlorides and oxychlorides, for instance by the process to be hereinafter described, the said metals and alloys are particularly well adapted for forging. rolling and the like, and the good preserployed as t e raw material is lowered by the addition of calcium and of a suitable flux; the chlorides and oxychlorides are elimlnated by stirring the mass in the presence of a chemical agent which may be so chosen as to simultaneously act as a flux; the surface of the metal is protected against oxidation by the use of a layer of a reducing agent which also effects the reduction of all oxide impurities on the surface of the metallic bath.

I prefer to place the magnesium metal or alloy serving as the raw material in a crucible which is preliminarily sprinkled with magnesium fluoride MgFh; this latter substance will be further distributed among the ieces of metal and also spread upon the surace of the metallic mass. As soon as the metal commences to melt, the mass is vigorously stirred in order to form an intimate mixture of the said metal and the magnesium fluoride. This latter acts both as a flux and as a purifier. It imparts fluidity to the magnesium or its alloys, and eliminates the chlorides and oxychlorides which rise to the surface of the bath.

When the metallic mass has become sufiiciently fluid, I incorporate therein the amount of the calcium which is desired according to the required properties of the metal; I prefer to add the calcium in the form of very small particles, for this state conduces to the rapid diffusion of the calcium throughout the magnesium, and the reaction even takes place with such violence that a vigorous stirring of the mass results, this being most favorable for the intimate contact of the various constituents.

The small pieces of calcium can be for instance placed in a thin magnesium tube and the latter introduced into the center of the mass; the tube is soon melted, and the calcium at once dissolves in the bath, which boils up to a considerable degree.

The surface of the metal bath is then sprinkled with a reducing agent such as ammoniuln chloride NI-LCI, which forms a crust on the surface and thus protects the metal bath against the oxygen of. the air and PI'G'. vents all excessive oxidation of the same; at the same time the ammonium chloride reduces the oxides and ox chlorides which may have been formed or w iich have risen to the surface. In this manner, and without any ignition or excessive oxidation. a metal or alloy having magnesium as a base is produced, which contains no zinc but contains calcium, and is freed from its prejudicial impurities and chiefly the chlorides and oxychlorides.

When magnesium of a moderate grade of purity is employed as raw material, I prefer to adopt the following proportions of the chemical agents before mentioned:

For kg. of magnesium 30 to grammes of magnesium fluoride and 30 to grammes of ammonium chloride.

These quantities can be doubled or even tripled specially for the magnesium fluoride, if the raw magnesium contains a great deal of impurities. In the appended claims, the expression metallic magnesium material is intended to cover magnesium itself, as well as alloys of magnesium.

I claim:

1. The process of purification of magnesiuin or its alloys which comprises forming complexes with the oxychlorides and oxides found in the bath by mixing same with magnesium fluoride acting as a main purifier, without adding a chloride, and collecting the complexes at the surfaceof the bath.

2. Process according to claim 1, consisting in roducing the agitation of the bath by the ad ition of calcium in a finely divided condition.

3. Process according to claim 1 consisting in producing the agitation by the addition offinely divided calcium enclosed in a cartridge of magnesium.

4. Process according to claim 1 consisting in also adding to the bath ammonium chloride to produce a reducing layer on the surface of the bath.

5. Process for purification of magnesium or its alloys consisting in adding magnesium fluoride to the bath, then incorporating finely divided calcium into the mass, and placing a layer of ammonium chloride on the surface of the bath.

In testimony whereof I have signed my name to this specification.

. GILBERT MICHEL. 

